The present invention relates to a developing device for developing an electrostatic latent image formed, by using an electrophotographic copying process or the like, on a surface of an electrostatic latent image support member.
A developing device has been proposed in, for example, U.S. Pat. No. 4,615,606. In this known developing device, a two-component developer composed of toner and carrier is held in a state of a magnetic brush on a surface of a developing sleeve having a magnetic roller incorporated therein. Then, upon rotation of the developing sleeve, the magnetic brush rubs against a surface of an electrostatic latent image support member such that the electrostatic latent image is developed into a visible image. Furthermore, in order to replenish the developing sleeve with the toner in amount corresponding to that of the toner consumed for development, there are provided at a bottom opening of a toner hopper disposed at a rear side of the developing sleeve, a toner supply roller confronting the developing sleeve and formed, on its surface, with minute recesses and a blade held in pressing contact with the toner supply roller. Thus, upon rotation of the toner supply roller, the toner received in the minute recesses is carried to a region where the toner supply roller and the developing sleeve confront each other, while at a portion of the toner supply roller where the blade is held in pressing contact with the toner supply roller, electric charge is imparted to the toner filled in the minute recesses. However, the above described U.S. Patent merely suggests that the minute recesses have a depth of 10 microns or more and does not disclose the minute recesses in more detail.
Therefore, if each of the minute recesses referred to above is simply formed by a cavity 50 having a smooth surface as shown in FIG. 5, a coefficient of friction between the toner and the surface of the cavity 50 is small. Thus, when the toner held on the toner supply roller passes by the blade, the toner is pushed to a downstream side of the cavity 50 by the blade and thus, is aggregated and set by a pressing force of the blade, thereby resulting in reduction of a volume of the cavity 50. Hence, the known developing device has such drawbacks that concentration of a copied image drops due to lack of amount of the toner supplied to the developing sleeve and quantity of electric charge imparted to the toner and fog occurs in the background of the copied image.